Hi Floyd
On (22 May 96) Floyd Williams wrote to All...
 FW> Anyone have the coefficient for the rate of heat absorption per
 FW> square foot of black surface exposed to the sun? Or even better:
 FW> how big does a passive solar water heater have to be
 FW> (a practicable size and rate of heating) to supply 100 gallon of hot
 FW> water per day.
Sorry, don't know the Black Body factor- it will be found in basic physics
texts no doubt. The number is a bit misleading as there are large
discrepancies between the theoretical, and what is practically achieved.
In Australia, roof top HW systems are very common. The storage tank is often
integrated with the collector, and an elec booster element is provided. The
booster is usually manually switched from inside the house. If you have
overnight guests, or if the weather has been very cloudy then the booster 
ill
usually be "on".
I guess that the collector area for a family home, is around 1.5 to 4 sq
yards. The collector is a fixture, the steerable arrangement [to face the sun
directly] is extremely rare.
There are advantages/ disadvantages to consider-
* The water is coldest when you may need it most ie in the morning when
laundry, shower baths are in use. The water is hottest when you need it least
ie at tea time. Therefore the thermal losses, are substantial in relation to
what is collected. Really good insulation of the pipework is essential and
this can make retrofitting, a big problem.
* In rural districts where energy costs are high, the system can be a winner
$$$ saved. Especially if the local generating station is diesel powered, or 
f
there is neither gas nor elec Utility service.
* In urban sites where energy is cheapest and aesthetics apply, you may have
difficulty picking a good location for the collector. Not nice if it is later
overshadowed by neighbours' trees, or new construction next door. Architects
hate the rooftop hardware that is needed. Owners often prefer to have the 
house
front facing the sun!!
* For a young home owner building on a lot where they will spend many years,
great idea. The higher capital costs can be recovered later, as saved energy
bills.
* For an older person [me] the HW system may outlive me so the lowest capital
cost option, is attractive. Our elec rates here are so low [discounted more
than 50% for off-peak] that the cash cost of a solar system, if invested in a
secure Bank interest bearing deposit will earn more in interest than I have 
o
pay for the hot water elec bill. And my capital remains on deposit, 
iminished
only by inflation....... whereas and expensive HW system will deteriorate and
eventually become worthless junk.
There are thus monetary, and also emotional forces that drive our choice. 
act
is, that many people willingly opt [emotionally] for the responsible choice 
f
defending the environment, and buying solar as good citizens. Great- it makes
them happy, and is less damaging to my lifestyle.
^^^^                                ^^
                               ^^^^^^^^^^
My Mom told me of a US family who baptised their baby Citronella. We laughed!
because in AUS at that time, citronella was an oil used for warrring against
insects, before DDT etc had been marketted.  Cheers....ALEC
... ........BUNDANOON, on a dirt track leading to the Info Superhighway
--- PPoint 1.92
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